This disclosure relates generally to display devices, in particular to improving light extraction for display devices.
Head-mounted displays (HMDs) can include an electronic display such as an Organic Light Emitting Diode (OLED) display. One problem with using electronic displays in an HMD is the screen door effect, in which non-emissive areas separating subpixels or pixels of a display device become visible in the displayed image. In an OLED display, there is significant loss in light extraction from the OLED pixels due to optical properties of layers used to form an OLED display such as organic material, a cover glass, and air. For example, the index of refraction of organic material is greater than index of refraction of the cover glass which is greater than the index of refraction of air. When light from an emitting layer of the organic material is incident on the cover glass at a shallow angle to the surface of the cover glass, the light may experience total internal reflection at an interface between the organic material and cover glass surface or at an interface between the cover glass and air. Thus, this light is reflected back towards the organic material and does not exit out of the OLED display. As such, this light is wasted and does not contribute to improving the efficiency of the display.